As per post 48. Redding is saying their 280ai is different than a 280rem imp. 2 different cartridges. An improved can be any length you want. An AI is specifically made .004 short of parent cartridge. Post 49. I never said any Reamer prints we're wrong. I said gunsmiths don't chamber to the numbers on them. We use Sammi spec guages to make a chamber the correct depth. So if I'm using a Sammi spec 280ai guage and a standard 280 go guage as a no go and they both give me the same depth than I conclude it's the same chamber. The Reamer is cut the same and it's the same depth in the barrel. The intent of making the chamber .004 shorter from Ackley was so parent brass would have a crush fit and be easier to fireform. Now if nosler made the chamber another .014 shorter that's .018 shorter than parent brass. A standard 280 brass would never fit in a nosler chamber. Yet they do fit with a slight crush fit. Just like the Ackley is supposed to.
Shep
We agree that P.O. Ackley wildcats off the parent cartridges are designed from a headspace 0.004" shorter than the headspace datum on the parent SAAMI cartridge? If so, let's continue with that as a precept, a principle set in concrete. Engineers might call this as an established design parameter.
I will provide the description of the math (largely tedious trigonometry) I used to calculate the headspace for the SAAMI "280 Remington (7mm Express Remington)", after wildcatting to P.O. Ackley's version of the 280 A.I.
I start with the SAAMI "280 Remington" minimum chamber headspace dimension of 2.100" at the 0.375" shoulder diameter datum off the SAAMI drawing. I subtract 0.004" from that dimension. 2.100" minus 0.004" equals 2.096" headspace at the 0.375" datum on the 15 degree, 15 minute shoulder angle on the "280 Remington" SAAMI minimum chamber drawing. I then process the math (primarily tedious trigonometric calculations) to convert the "280 Remington" parent chamber (minus 0.004" on the shoulder) into a 40-degree shoulder. The mathematical transformation of the shoulder angle begins at the neck/shoulder junction of the SAAMI "280 Remington" (minus 0.004"). A 40-degree shoulder from that neck/shoulder junction continues back toward the case body until it meets with the (now) lengthened case body, at the enlarged shoulder diameter specified on the SAAMI "280 Ackley Improved". This shifts the case body/shoulder junction forward from it's parent cartridge. The shoulder is mathematically transformed from 15 degrees, 15 minutes, to 40 degrees in this manner. I repeated the math calculations multiple times, and consistently reach a headspace dimension from the case head to the 0.375" datum on the transformed (Ackley-ized) 40-degree shoulder
0.014" (plus or minus a 0.0001-0.0003")
longer than the SAAMI "280 Ackley Improved" minimum chamber headspace. Both the SAAMI "280 Remington" and "280 Ackley Improved" drawings measure headspace from the case head to the identical 0.375" diameter datum on the shoulders. Can't be any more straightforward, simpler, or verifiable. My calculations replicate the findings of Redding Reloading Company on their website, and the multiple other sources/references provided in my prior post.
Math removes the uncertainties of the QA/QC (correctness) of manufactured go-gauges, and the how those gauges get used to cut and measure chambers. Math can be vetted by others, with the sharing and proofing of calculation sheets. Nobody can vet the dimensions of others' go-gauges unless they have the gauges in hand, and measuring equipment sophisticated and precise enough to guarantee accurate measurements are collected at the proper locations.
My proposal? Run the math as I describe above. The beginning headspace dimension is 2.096"at the 0.375" datum (0.004" less than the SAAMI "280 Remington" minimum chamber headspace dimension). This means the case head to neck/shoulder junction is also reduced by 0.004" from the SAAMI "280 Remington". The shoulder angle transformation to 40-degrees begins at this distance from the case head. I understood you agree this is consistent with a traditional Ackley wildcat cartridge, as P.O. Ackley intended and consistently practiced.
Should you (or anyone of your choosing) perform this math, and conclude the calculated headspace from the case head to the 0.375" datum on the converted/transformed 40-degree shoulder
is less than 0.013" longer than the current SAAMI "280 Ackley Improved" minimum chamber headspace dimension at the 0.375" datum, provide images of your calculation sheets. I'll spend the time to review those calculation sheets. I see a competent and good faith effort at the math, I'll compare that math to my own calculations. It should be possible to settle this matter, with a straightforward mathematical analysis. Provided... we accept the premise that math can, and does, precede the establishment of SAAMI cartridge standards, drawings, and dimensions. Math sets the foundation of every SAAMI cartridge standard. Without it there could be no meaningful SAAMI standards. If you're gonna throw the math away if it doesn't reach your required endpoint, don't waste your time, or mine.
Well? I'm up for it.
